Few comedies can successfully turn physics into punchlines, but with three seasons under its utility belt and another three commissioned by CBS, The Big Bang Theory hits its fourth year on DVD with a confident and unashamedly nerdy stride.

There’s a noticeable ease among the principal cast now and it translates into a great sense of fun onscreen: jokes are exchanged with greater fluidity, the banter is sharper, and everyone has settled into their character and is now focusing on developing their foibles and habits.

Season 4 pushes our favourite geeks into new territories that often jar with their quiet world of comic books and particle colliders and it all leads to bigger laughs for the audience. Slimy ladies-man wannabe Howard (Simon Helberg) must navigate the pitfalls of having a long-term girlfriend, Leonard (Johnny Galecki) begins a new relationship that puts him at odds with friend Raj (Kunal Nayyar), and in the stand-out arc of the season, Jim Parson’s Sheldon Cooper encounters his female double, Amy Farrah Fowler, played with deadpan brilliance by Mayim Bialik.

Her inclusion as part of the main cast is a smart move and injects new life into the show, not simply because she is a wonderfully drawn character, but because of what she brings out in the others. The interplay that ensues in the bizarre ‘relationship’ between herself and Sheldon manages to reinforce the aloofness and social awkwardness that the audience has come to love in him, a man who makes Mr. Spock look like Casanova.

Her presence also rescues Penny (Kaley Cuoco) from the danger of becoming a one-note nerd-antagoniser, and watching Amy bond with her new “bestie” across the season is simultaneously weird and heartwarming. It’s like seeing a robot befriend a pony.

As the show has improved so has the calibre of guest stars, and there are familiar faces aplenty who’ll please sci-fi fans of all denominations. Trekkies are especially rewarded by appearances from Enterprise alumni George Takei, Levar Burton and Wil ‘Wesley’ Wheaton, the latter returning to play a marvellously hammed-up version of himself.

With plots that include depraved uses for robot arms, App-designing and ill-fated attempts at immortality, The Big Bang Theory rarely falls into the standard comedy clichés, and even when the odd well-worn scenario comes along the nature of the characters means a new spin can always be put on the old (see Sheldon’s logically insane reaction to a break-up in ‘The Zazzy Substitution’).

No matter how outrageous some of the situations may become, the incredibly strong writing and performances mean that we still care about these loveably weird characters, even if – in one case – their privates end up trapped in the grasp of a robot hand. And surely that’s the mark of any good comedy.

Extras: Special features here are as scare as a Higgs-Boson; ‘The Big Bang’s Theory of Relativity’ features members of the cast asking one another questions, which is a nice spin on the usual format and proves to be interesting. There’s also a music video for The Big Bang Theory‘s theme song, which is worth listening to just to hear Barenaked Ladies manage the impressive feat of rhyming ‘Australopithecus’ with something.

Finally, if you’ve ever laid awake at night wondering just what The Barenaked Ladies themselves think of the show, you can find out in ‘Barenaked Ladies on The Big Bang Theory’ (hint: they like it). All in all though, a poor showing for such a popular programme.

Released on DVD on Monday 12th September 2011 by Warner Home Video.

> Buy the DVD boxset on Amazon.

Watch the Season 4 trailer…